Antonio Conte was left frustrated by Napoli despite their 2-1 victory over Genoa, conceding "I did not like a single thing about the second half".
With Atalanta not in action until Sunday, the Partenopei took full advantage to leapfrog Gian Piero Gasperini's side to the Serie A summit.
The damage was done during the first half as headers from Frank Anguissa and Amir Rrahmani rendered Andrea Pinamonti's strike early in the second half academic.
However, Napoli had Alex Meret to thank for preserving the three points, with the goalkeeper making a string of smart saves to keep the hosts at bay.
And Conte insists his players must improve the consistency of their performance levels if they are to genuinely challenge at the top of the table.
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"If you only see the result and three points, you don't build anything," he told DAZN. "Our first half was our best of the season, and I really did not expect the second half to be like that. Maybe, I felt it in the locker room at half-time.
"The players need to realise they must play from start to finish, with their foot on the gas at all times. I did not like a single thing about the second half. Defend by attacking, that has to be our mantra.
"I have players who know where they need to improve, and they will go home disappointed today at almost throwing away three points.
"If we want to have the least bit of ambition and be up there causing trouble for the top spots, then we need to be on it for 95 minutes."
Meanwhile, Genoa saw their six-match unbeaten streak come to an end, while they suffered their first defeat under Patrick Vieira, who was still pleased with his side's efforts.
"We showed that we could play good football but, in the end, we did not take any points," he said. "After the game, I told the boys that if we continue to do as we did in the second half, we will win more games.
"It was a first half where we didn't play the way we wanted to play. But I think the quality of the opponent also put the team in difficulty.
"In the second half, we were more aggressive, we grew, and I think the team deserved the point. I feel sorry for the players."